In many injection molding operations, there is a need to utilize a movable valve pin to open and close a gate into a mold cavity in order to control the melt flow into the mold cavity. In some cases, however, the material that is being molded can be corrosive or abrasive and can degrade the valve pin as the material flows thereby. As the valve pin degrades, its ability to seal the gate is gradually and progressively reduced, until an effective seal is unable to be made. The injection molding apparatus must then be stopped and the valve pin must be repaired or replaced, which can be an expensive and time consuming procedure. For such operations, the valve pins can have an undesirably short operating life.
An example of the above described situation occurs in metal injection molding, for magnesium injection molding in particular. Due to the relatively high flowability of magnesium and due to its corrosiveness, leakage or drool can occur at the gate relatively quickly as a result of abrasion of the valve pin.
Thus, there is a need for a new gating system for an injection molding apparatus, that provide improved reliability and longer operating life for the valve pin.